1. Technical Field
The present invention relates to a liquid-ejecting head and a liquid-ejecting apparatus having the same. Specifically, the invention is usefully applied to form a fluid-resistant protection film on a surface of a channel for a liquid that may etch the channel.
2. Related Art
An ink-jet recording apparatus is known as a liquid-ejecting apparatus. The ink-jet recording apparatus includes a plurality of pressure-generating chambers that generate pressure for ejecting ink droplets with a piezoelectric element or a heater element, a common reservoir for supplying an ink to each pressure-generating chamber, and an ink-jet recording head provided with nozzle openings being communicated with the respective pressure-generating chambers. Such an ink-jet recording apparatus ejects an ink droplet from a nozzle opening by applying an ejection energy to an ink in the pressure-generating chamber being communicated with the nozzle corresponding to a printing signal.
The ink-jet recording head is roughly classified into a piezoelectric vibration-type in which each of the pressure-generating chambers is partially made of a vibration plate and an ink droplet is ejected from a nozzle opening by deforming the vibration plate with a piezoelectric element and into a system in which a heater element such as a resistance heating wire that generates Joule heat according to a driving signal is disposed inside each of the pressure-generating chambers and an ink droplet is ejected from a nozzle opening by means of a bubble generated by the heater element.
In these known ink-jet recording heads, the pressure-generating chambers are generally formed on a silicon substrate. If an alkaline ink is used, the ink gradually dissolves the silicon substrate and, thereby, the width of each pressure-generating chamber changes with a lapse of time. This causes a change in the pressure that is applied to the pressure-generating chamber by driving a piezoelectric element or a heater element, resulting in a gradual deterioration in the ink ejection characteristics.
In order to solve the above-mentioned problems, it is proposed to form a film having hydrophilicity and alkali resistance, such as a nickel film, inside the pressure-generating chambers for preventing the silicon substrate from being dissolved in the ink (refer to, for example, FIG. 1 and paragraph [0020] of JP-A-10-264383).
However, such a nickel film is poor in long-term stability. Accordingly, in order to solve this problem, a tantalum oxide film is proposed as the protection film (refer to, for example, FIG. 1 and paragraph [0032] of JP-A-2004-262225). The above-mentioned protection films are each formed as an amorphous film for good adhesion to the silicon substrate. That is because a crystallized film has a high stress of its own and, thereby, the adhesion is generally low.
However, the known protection films described above have a single amorphous layer structure and may hence have pinhole defects. Therefore, the protection film is required to have a thickness excessively large, in order to avoid the occurrence of pinhole defects. Since a protection film having a larger thickness tends to inhibit displacement of a piezoelectric element and therefore badly affects the vibration characteristics of the piezoelectric element.